This invention relates to a bake/chill station for processing semiconductor wafers in the production of circuit chips, and more particularly to a bake/chill station wherein no intermediate handling step is required.
The processing of semiconductor wafers in the manufacture of circuit chips requires precise bake and subsequent rechill of the wafers, in order to cause a layer of material applied to the top surface of the wafer to set or harden.
The bake and chill steps are usually performed by separate bake plates and chill plates, with a mechanical move of the hot wafer between the plates. Such an approach presents a number of problems. First, the handling required by the mechanical move introduces the possibility of contamination of the wafer. Second, throughput of the manufacturing process is reduced, because of the mechanical move required between the plates. Third, the time of the bake cycle and the time of the chill cycle can not be precisely controlled, because of the time required to move the wafer to and from the respective plates. Fourth, the cost of equipment is higher than it need be, because the bake and chill plates are not integrated into one housing.
The bake plate is usually positioned below the wafer, so that the back side of the wafer is heated. Although this may reduce contamination of the top surface of the wafer, on which the desired material is layered, such positioning introduces other problems. Because of the toxic nature of solvents used for applying material to the surface of the wafer, such solvents must be prevented from escaping into the atmosphere. This is usually done by enclosing the bake plate and wafer in a process chamber and capturing the escaping solvent vapors. However, the lid of the process chamber will be the same temperature or cooler than the wafer, and therefore escaping solvent vapors can condense on the lid, and over a period of time this condensation produces solid particulates that may contaminate the surface of the wafer. Therefore, the lid needs to be cleaned periodically. Furthermore, because the bake plate is below the wafer, heated air tends to rise and generate convection currents that are very destructive to temperature uniformity.